1. Field of the Invention
The present invention relates to a jig for use in a semiconductor test and a method of measuring a breakdown voltage by using the jig. More specifically, the present invention relates to a jig for use in a semiconductor test and method of measuring a breakdown voltage by using the jig that are suitably applicable for measuring the breakdown voltage of a wide bandgap semiconductor.
2. Description of the Background Art
A power semiconductor device using a wide bandgap semiconductor being a semiconductor with a high breakdown voltage is subjected to measurement of electrical characteristics (hereinafter also called a test) when the power semiconductor device is in the form of a chip and has not been implemented on a package. Measurement items of electrical characteristics include measurement of a breakdown voltage. A breakdown voltage is considered as one of important indicators of performances, and should always be measured.
The electrical characteristics of a chip of a power semiconductor device (hereinafter also called a semiconductor chip) with a high breakdown voltage are generally measured in the conventional system as follows, for example. In this system, a probe pin comes into contact with a surface of a semiconductor chip placed on a stage and then a voltage is applied, thereby testing (measuring) electrical characteristics (see Japanese Patent Application Laid-Open No. 2006-337247 (FIG. 10), for example). In a different system of measuring the electrical characteristics of a semiconductor wafer (chip), the semiconductor wafer is dipped into an insulation solution (see Japanese Patent Application Laid-Open No. 2003-100819 and Japanese Patent Publication No. 4482061, for example).
A power semiconductor device with a high breakdown voltage has a breakdown voltage of several hundred volts, and a distance between an electrode formed on a semiconductor chip and an edge portion of the chip is short. So, in the system of Japanese Patent Application Laid-Open No. 2006-337247, if a high voltage is applied to the probe pin contacting a surface electrode on the semiconductor chip and to the stage contacting a back electrode on the semiconductor chip for measurement of the breakdown voltage of the semiconductor chip, insulation breakdown is generated between the surface electrode on the semiconductor chip and the stage. This generates discharge in atmosphere (atmosphere discharge or creeping discharge), leading to a problem of breakage of the semiconductor chip and breakage of a power supply of the measuring system.
Atmosphere discharge is affected by a creeping distance, air clearance, humidity, temperature and pressure of atmosphere, moisture absorption with a protective film formed on a surface of a semiconductor chip, and the like. So, generation of atmosphere discharge makes it impossible to measure a breakdown voltage accurately. As a result, even a semiconductor chip with inaccurate breakdown voltage characteristics cannot be evaluated (breakdown voltage thereof cannot be measured accurately) before the semiconductor chip is assembled into a package. This leads to serious reduction in measurement efficiency.
Materials of a wide bandgap semiconductor such as silicon carbide and gallium nitride have an insulation breakdown electric field of one order of magnitude greater than that of silicone. This makes it possible to shrink a terminal structure of a chip provided to maintain a breakdown voltage securely. As a result of shrinkage of the terminal structure, the insulation breakdown electric field of atmosphere extending from an opening edge of a protective film formed at a terminal portion to an edge portion of a chip is made smaller than insulation breakdown electric field in bulk, leading to a problem in that creeping discharge is generated easily. There has also been a problem in that discharge easily damages a gate oxide film of a semiconductor device having an MOS (metal-oxide semiconductor) structure.
The techniques suggested in Japanese Patent Application Laid-Open No. 2003-100819 and Japanese Patent Publication No. 4482061 are intended to avoid influence on a semiconductor chip exerted by the aforementioned discharge. However, these techniques involve a unit for supply and drainage of an insulation solution. This entails costs so the electrical characteristics of a semiconductor chip cannot be measured at low cost.